1. Field of the Invention
The present invention relates to a method for stably preparing an isothiocyanate or isothiocyanate (hereinafter referred to as an isothiocyanate product) in a sufficient amount in a high yield from a natural cruciferous plant material such as wasabi, horseradish, watercress or the like as a starting material by effecting sufficient enzymatic reactions. More particularly, it relates to a method for stably preparing an isothiocyanate product containing no substantial pungent ingredient in a sufficient amount in a high yield from a natural cruciferous plant material.
In the present invention, an isothiocyanate product containing allyl isothiocyanate as a pungent ingredient is referred to as “isothiocyanate (A)”0 and an isothiocyanate product containing no substantial allyl isothiocyanate as a pungent ingredient is referred to as “isothiocyanate (B)”.
The isothiocyanate (B) according to the present invention, per se or after processed, is utilized in processed foods containing isothiocyanate (B) which is difficult of ingestion in a large amount and from which the highly irritating pungent ingredient has been removed.
In this specification, “pungent ingredient is removed” means “pungent ingredient is removed to such a degree that a person who ingests isothiocyanate (B) feels no substantial irritation or no irritation at all” and does not necessarily mean “pungent ingredient is completely removed”, and likewise, “containing no pungent ingredient” means “containing a pungent ingredient in such a amount that a person who ingests isothiocyanate (B) feels no substantial irritation or no irritation at all” 0 and does not necessarily mean “containing no pungent ingredient at all”.
2. Description of the Prior Art
It is known that cruciferous plants such as wasabi, horseradish, watercress and the like are rich in isothiocyanates which exhibit excellent activities as health foods. For example, allyl isothiocyanate and 4-methylsulfinylbutyl isothiocyanate which are contained in wasabi, mustard and the like in large amounts exhibit antibacterial activity and carcinogenesis preventing activity, respectively. It is also known that 6-methylthiohexyl isothiocyanate which is contained in wasabi exhibits platelet aggregation inhibiting activity. Further, it is known that 6-methylsulfinylhexyl isothiocyanate which is one of isothiocyanates contained in wasabi exhibits high GST inducing activity relating to antibacterial activity, carcinogenesis preventing activity and metabolic detoxification activity.
However, isothiocyanates including the above-mentioned 6-methylsulfinylhexyl isothiocyanate are present in wasabi in the form of glucosinolate. Accordingly, in order to make effective use of isothiocyanates, it is necessary that decomposition reaction of glucosinolate be effected by destroying cells of wasabi, for example, grating wasabi.
By grating wasabi, however, allyl isothiocyanate as highly irritating pungent ingredient is formed in a large amount. Accordingly, it is extremely difficult to ingest 6-methylsulfinylhexyl isothiocyanate as an active ingredient in a large amount. Consequently, it is difficult to ingest 6-methylsulfinylhexyl isothiocyanate in such an amount that the activity thereof can be expected.
As mentioned above, it is known that cruciferous plants such as watercress and the like are rich in isothiocyanates. However, isothiocyanates such as 6-methylsulfinylhexyl isothiocyanate is highly reactive with water, ethyl alcohol or the like and is susceptible to heat, oxygen or the like. Accordingly, for example, during cooking, most of 6-methylsulfinylhexyl isothiocyanate degraded. It has been, therefore, difficult to stably provide 6-methylsulfinylhexyl isothiocyanate in a large amount.